1. Field of Invention
This invention relates to integrated circuit processes and more particularly to a method of forming zones or junctions in the formation of transistors in the like.
2. Prior Art
In the manufacture of integrated circuits, the formation of certain zones, such as the buried collector, in the semiconductor substrate is conventionally formed by a diffusion or by an ion implantation process both of which tend to damage the surface of the substrate requiring a healing by a subsequent heat treatment before the manufacturing process can be completed. In the case of a buried collector, for example, a damage to the surface of the substrate must be healed before an epitaxial layer can be formed on the substrate.
The U.S. Patent to Graul et al U.S. Pat. No. 4,063,967 taught that the damage to a substrate surface can be eliminated by selectively positioning polycrystalline or amorphous, hereinafter called polysilicon, layers onto selected surface areas defined by windows in a mask, ion implanting a dopant into such layers and later diffusing the dopant from the layers into the selected areas on the semiconductor substrate. In the patented process, the patentee took advantage of the polysilicon layer by using it as an ohmic conductor complimenting the metallized material formed thereover and thus avoided any problem in removing the polysilicon layer.
In the manufacture of circuits the removal of the polysilicon layer is desirable, as for example in the formation of a buried collector zone, for the formation of the epitaxial layer over the semiconductor substrate to form the buried collector. This advantage of removing the polysilicon layer is not in the prior art.
Accordingly, it is a principal object of this invention to provide in the process of manufacturing integrated circuits the steps of forming and removing a polysilicon layer such that buried collector and other junctions may be formed in a substrate without damage to the surface.